f F, N, and Si elements. The F and N came from the precursor solution, and the amount of F decreased with increasing calcination temperature. Two sources of Si were identified. One was from the SiF6 2-ions, which were formed by a reaction between the treatment solution and quartz substrate. The other was attributed to the diffusion of Si from the surface of quartz substrate into TiO2 thin film at 700℃ or higher calcination temperatures. With increasing calcination temperature, the photocatalytic activity of the TiO2 thin films gradually increased due to the improvement of crystallization of the anatase TiO2 thin films. At 700℃, the TiO2 thin film showed the highest photocatalytic activity due to the increasing amount of SiO2 as an adsorbent center and better crystallization of TiO2 in the composite thin film. Moreover, the SiO2/TiO2 composite thin film showed the lowest PL intensity due to a decrease in the recombination rate of photogenerated electrons and holes under UV light irradiation, which further confirms the film with the highest photocatalytic activity at 700℃. When the calcination temperature is higher than 700℃, the decrease in photocatalytic activity is due to the formation of rutile and the sintering and growth of TiO2 crystallites resulting in the decrease of surface area.